1. Field of the Invention
The present invention relates to a display apparatus in which self luminous elements are arranged in a matrix form, and a method for driving the same.
2. Description of the Related Art
In display apparatuses of CRT, liquid crystal, organic EL and the like, a refresh operation of rewriting a video frame to be displayed several tens times in one second is performed, and the frame rewrite frequency is called a refresh rate. When the refresh rate is low, a flicker (flickering) occurs. Therefore, the refresh rates of these display apparatuses are usually set at the frequency (60 Hz) at which flickers do not occur. An organic EL display apparatus uses a self luminous display element for each pixel, and emits light and displays an image by passing a current to each of the light emitting elements. The brightness of the display screen can be set according to the light emitting time and light emitting intensity in one frame. Depending on the frequency of light emission, and the ratio (duty ratio) of the light emitting time and non-light emitting time in one frame, human eyes visually recognize the difference of light emission (bright part) and non-light emission (dark part), and recognizes the difference as a flicker (flickering) of the display screen. Accordingly, even if an image is displayed at the refresh rate of 60 Hz, a flicker of the display screen occurs depending on the duty ratio, and the display quality is degraded. Japanese Patent Application Laid-Open No. 2006-30516 discloses the drive method that suppresses a flicker by using a duty drive method that controls the brightness of the display screen according to a duty ratio.
However, when on-off drive is performed with a certain duty ratio according to the method for driving the display apparatus described in Japanese Patent Application Laid-Open No. 2006-30516, the total current amount that flows into the display region varies according to time, and the current variation acts on the power supply impedance having a finite value and brings about a power supply variation. When one field (or one frame) is divided into a plurality of sub fields (or sub frames), and the light emitting period is divided, the power supply variation and the light emitting period are synchronized with each other, and a luminance variation occurs to the display region. As a result, there arises the problem of causing degradation of image quality.
Thus, the present invention relates to a display apparatus that performs periodic on-off drive, and has an object to provide a method for driving a display apparatus that performs favorable display in which degradation of image quality caused by a power supply variation is suppressed.